Bit shifting in Fauna

bit_shifting_in_fauna.js

// try out some bit shifting!!

// All you really need is to multiply or divide by a power of 2
// Make sure to wrap the `Pow` function in `ToInteger`


/*
 * Shift a little bit
 */

Let(
  {
    int: ToInteger("5188146770730811392"),
    shift: 1,
    multiplier: ToInteger(Pow(2, Var("shift"))),
    shift_left: Multiply(Var("int"), Var("multiplier")),
    shift_right: Divide(Var("int"), Var("multiplier")),
  },
  [
    Format("int:         0x%x :: 0b%s :: %d", Var("int"), Call("PrintBinary", Var("int")), Var("int")),
    Format("shift_left:  0x%016x :: 0b%s :: %d", Var("shift_left"), Call("PrintBinary", Var("shift_left")), Var("shift_left")),
    Format("shift_right: 0x%016x :: 0b%s :: %d", Var("shift_right"), Call("PrintBinary", Var("shift_right")), Var("shift_right")),
  ]
)

// returns
[
  "int:         0x4800000000000000 :: 0b0100100000000000000000000000000000000000000000000000000000000000 :: 5188146770730811392",
  "shift_left:  0x9000000000000000 :: 0b0001000000000000000000000000000000000000000000000000000000000000 :: -8070450532247928832",
  "shift_right: 0x2400000000000000 :: 0b0010010000000000000000000000000000000000000000000000000000000000 :: 2594073385365405696"
]

/*
 * Shift a lot
 */

Let(
  {
    int: ToInteger("5188146770730811392"),
    shift: 59,
    multiplier: ToInteger(Pow(2, Var("shift"))),
    shift_left: Multiply(Var("int"), Var("multiplier")),
    shift_right: Divide(Var("int"), Var("multiplier")),
  },
  [
    Format("int:         0x%x :: 0b%s :: %d", Var("int"), Call("PrintBinary", Var("int")), Var("int")),
    Format("shift_left:  0x%016x :: 0b%s :: %d", Var("shift_left"), Call("PrintBinary", Var("shift_left")), Var("shift_left")),
    Format("shift_right: 0x%016x :: 0b%s :: %d", Var("shift_right"), Call("PrintBinary", Var("shift_right")), Var("shift_right")),
  ]
)

// returns
[
  "int:         0x4800000000000000 :: 0b0100100000000000000000000000000000000000000000000000000000000000 :: 5188146770730811392",
  "shift_left:  0x0000000000000000 :: 0b0000000000000000000000000000000000000000000000000000000000000000 :: 0",
  "shift_right: 0x0000000000000009 :: 0b0000000000000000000000000000000000000000000000000000000000001001 :: 9"
]

PowersOf2.fql.js

// UDF to create an array of 2^0 to 2^62
// Fauna uses signed integers, so 2^64 isn't something we can work with
Query(
  Lambda(
    [],
      Map(
        [
          0,
          1,
          2,
          3,
          4,
          5,
          6,
          7,
          8,
          9,
          10,
          11,
          12,
          13,
          14,
          15,
          16,
          17,
          18,
          19,
          20,
          21,
          22,
          23,
          24,
          25,
          26,
          27,
          28,
          29,
          30,
          31,
          32,
          33,
          34,
          35,
          36,
          37,
          38,
          39,
          40,
          41,
          42,
          43,
          44,
          45,
          46,
          47,
          48,
          49,
          50,
          51,
          52,
          53,
          54,
          55,
          56,
          57,
          58,
          59,
          60,
          61,
          62,
        ],
        Lambda("n", ToInteger(Pow(2, Var("n"))))
      )
  )
)

PrintBinary.fql.js

// Use the PowersOf2 method to print out the number bit by bit
// This would be WAY more efficient and cost effective (Transactional Compute Operations)
// to make a literal list of numbers, but this is easier to write!
// Remember that ints are signed, so we have to handle the signed bit separately
Query(
  Lambda(
    "int",
    Let(
      {
        number_part: Reduce(
          Lambda(
            ["acc", "val"],
            If(
              GT(Bitand([Var("int"), Var("val")]), 0),
              Concat(["1", Var("acc")]),
              Concat(["0", Var("acc")])
            )
          ),
          "",
          Call("PowersOf2", [])
        ),
        sign_part: If(GTE(Var("int"), 0), "0", "1")
      },
      Concat([Var("sign_part"), Var("number_part")])
    )
  )
)